1. Field of the Invention
The present invention related to a step-up step-down converter device which steps up or steps down an output voltage of a power supply facility having a fluctuated input voltage in a supply side of a photovoltaic power generation to a predetermined voltage so as to output, and more particularly to a step-up step-down converted device which can prevent reduction of power generation efficiency due to a dead zone generated at the step-up and step-down switching time on the basis of natural energy by a simple circuit structure.
2. Description of the Conventional Art
Since the solar panel voltage is widely changed according to the number of serial connections and the amount of received light in the power supply facility in which the supply power for the photovoltaic power generation is generally changed, a step-up step-down converter device is provided for stepping up or stepping down the input voltage to the predetermined voltage so as to output. For example, as shown in FIG. 9, a step-up step-down converter device 710 according to a prior art is connected to a solar panel 700 which generates electric power having direct voltage 0 V to 600 V by solar light, and is structured such as to step up and step down the voltage between 0 V and 600 V output from the solar panel 700 to a range between 0 V and 400 V so as to output.
The step-up step-down converter device is provided, as shown in FIG. 10, with two connection circuits which connect in series a switch A, an inductor and a switch D to a positive pole side of a closed circuit which is constructed between an input direct voltage Vin by the solar panel and an output side load RL, and connect a positive pole side circuit and a negative pole side circuit of the closed circuit via a capacitor C1 or C2, a connection circuit which connects from between the switch A and the inductor to the negative pole side circuit via a switch V, a connection circuit which connects from between the inductor and the switch D to the negative pole side circuit via a switch C, and a control circuit 8 which controls opening and closing of the switches A to D, and is structured such as to step up and step down the electric voltage output from the solar panel to the predetermined range by controlling the opening and closing of the switches A to D.
In the device mentioned above, since the voltage step-up operation and the voltage stepping down operation switch the value of the input voltage to the original one, there is generated a dead zone which can not be controlled due to a voltage detection error, a desired operation can not be obtained in the vicinity of the voltage, and there is generated a problem that the power generation efficiency is lowered.
In order to solve the problem mentioned above, a technique in patent document 1 has been proposed. The device employing the technique is provided, as shown in FIG. 11, with two connection circuits which connect in series a switch A, an inductor and a switch D to a positive pole side of a closed circuit which is constructed between an input direct voltage Vin by the solar panel and an output side load, and connect a positive pole side circuit and a negative pole side circuit of the closed circuit via a capacitor C1 or C2, a connection circuit which connects from between the switch A and the inductor to the negative pole side circuit via a switch V, a connection circuit which connects from between the inductor and the switch D to the negative pole side circuit via a switch C, and a control circuit 80 which controls opening and closing of the switches A to D, and is structured such that the control circuit 80 controls to open and close the switches A to D in response to the output voltage of the output load, thereby stepping up or stepping down the electric voltage output from the solar panel to the predetermined range so as to output.
The control circuit 80 is structured such as to be provided with a comparator a which inputs a detection voltage between a resistance R1 and a resistance R2 connected to the output voltage Vout supplied to the output side load as Vfb to a negative terminal, inputs a target voltage Vref to a positive terminal, and compares the detection voltage Vfb with the target voltage Vref so as to output an on-off signal VEA1, a comparator b which inputs the on-off signal VEA1 of the comparator a to the negative terminal, inputs a predetermined voltage Vp to the positive terminal, and compares the on-off signal VEA1 with the predetermined voltage Vp so as to output an on-off signal VEA2, a comparator c which inputs the on-off signal VEA1 to the negative terminal, inputs a predetermined voltage VY to the positive terminal, and compares the on-off signal VEA1 with the predetermined voltage VY so as to output an on-off signal VEA3, a circuit element e which selectively switches the on-off operation of the switches A and B on the basis of the on-off signal VEA3 from the comparator c, a comparator d which inputs a signal obtained by reversing the predetermined voltage VY at 180 degrees to the positive terminal, inputs the on-off signal VAE2 from the comparator b to the negative terminal, and compares the both so as to output an on-off signal VEA4, and a circuit element f which selectively switches the on-off operation of the switches C and D on the basis of the on-off signal VEA4 from the comparator d.
In the step-up step-down converter device structured as mentioned above, the control circuit 80 monitors the output voltage Vout supplied to the output side load in relation to the target voltage (for example, 400 V), and switches the step-down operation and the step-up operation so as to step down voltage in the case that the output voltage Vout is higher than the input voltage and step up voltage in the case that the output voltage Vout is lower than the input voltage. As a result, the step-up step-down converter operates to step up and step down the output voltage to a predetermined range (0 V to 400 V) so as to output without generation of the dead zone in principle at the switching time of the step-up and step-down operations.